A conventional direct current (DC) motor controller adapted to control a DC motor 19 is illustrated in FIG. 1. The DC motor controller has a first terminal 11 and a second terminal 12, and includes an upper limit switch 13, a lower limit switch 14, an upper diode 15 and a lower diode 16. The DC motor 19 is utilized to drive rotation of a screw rod (not shown) which urges linear movement of a nut (not shown).
The first terminal 11 and the second terminal 12 are configured to be connected to a polarity-switchable DC electric power source. For a positive configuration of the polarity-switchable DC electric power source where an electric potential applied to the first terminal 11 is higher than that applied to the second terminal 12, an electric current flows from the first terminal 11, through the DC motor 19, the upper limit switch 13 and the lower limit switch 14, and to the second terminal 12, in the given order. For a negative configuration of the polarity-switchable DC electric power source where the electric potential applied to the first terminal 11 is lower than that applied to the second terminal 12, the electric current flows in an opposite direction. By switching the polarity-switchable DC electric power source between the positive and negative configurations, the DC motor 19 is driven to operate in opposite directions to control the nut to move up and down along the screw rod. When the nut is moved up to an upper limit position where the upper limit switch 13 is triggered to an open state, the electric current is only allowed to flow in a direction from the second terminal 12, through the lower limit switch 14, the upper diode 15 and the DC motor 19, and to the first terminal 11. That is to say, the DC motor 19 is only allowed to be operated to control the nut to move down. Likewise, when the nut is moved down to a lower limit position where the lower limit switch 14 is triggered to an open state, the electric current is only allowed to flow in a direction from the first terminal 11, through the DC motor 19, the upper limit switch 13 and the lower diode 16, and to the second terminal 12, and therefore the DC motor 19 is only allowed to be operated to control the nut to move up.
However, since the upper limit switch 13, the lower limit switch 14, the upper diode 15 and the lower diode 16 are subjected to a high electric current flowing through the motor 19, large-sized devices that can bear the high electric current are required to implement the aforementioned components. Consequently, reduction in the physical size of the conventional DC motor controller is difficult to realize.